VHM Cylinder Head Insert for YAMAHA YZ 125 1996-2000

The VHM cylinder head insert is designed for YAMAHA YZ 125 from 1996 to 2000. The insert forms the combustion chamber of the VHM head. Its volume sets the engine's compression: a small volume gives more bottom end and mid-range, a larger volume keeps the engine smoother and longer-revving.

Key features

• Each version shows its three key figures: chamber volume, piston height and squish.
• Change the compression without machining the head, to suit the fuel and the terrain.
• Part number engraved on the insert.
• Fits VHM cylinder heads only.

Specifications

• Brand: VHM
• Manufacturer part numbers: AE32333-B, AE32333-C, AE32333-E, AE32333-F, AE32333-G
• Available versions: Version B (10.80 cc): ref. AE32333-B; Version C (11 cc): ref. AE32333-C; Version E (11.20 cc): ref. AE32333-E; Version F (11.40 cc): ref. AE32333-F; Version G (11.60 cc): ref. AE32333-G
• Engine: 2-stroke

Choosing the right version

Each version is defined by three dimensions: the chamber volume in cm³ (spark plug hole included), the piston height at top dead centre relative to the top of the cylinder (“−0.55”: piston 0.55 mm below the cylinder face) and the squish, the minimum gap between piston and insert. A smaller volume raises compression: more bottom end and mid-range, but a higher-octane fuel may become necessary.

When to change the insert?

• Switch to a different fuel (98 or race fuel with a higher octane rating).
• Engine knocking (pinking) or running hot: compression too high for the fuel.
• You want more torque on tight or sandy terrain.

Change the insert when you change fuel or type of riding, or if the engine pinks. The insert's three dimensions (volume, piston height, squish) must match your engine.

Fitting tips

1. The insert is changed with the cylinder head removed.
2. Check that the actual height of your piston at top dead centre matches the figure given for the insert.
3. Replace the VHM head O-rings every time you take it apart.
4. Check the squish with solder wire before riding.
5. Tighten the head to the recommended torque, in a criss-cross pattern and in several stages, then fit a new spark plug.

Why VHM?

Founded in 1995, VHM specialises in racing engine parts for motocross, road racing and karting. The brand started out with cylinder heads featuring interchangeable combustion chambers, which became its speciality, and then developed crankshafts, connecting rods and gasket kits.

Spare parts and items to plan

• VHM head O-rings : ATHENA M751802350094 · ATHENA M752006400094
• Spark plug : NGK 3530 · NGK 3230
• Coolant : LIQUI MOLY 1 L · TWIN AIR

Frequently asked questions

Will it fit my original cylinder head?
No: VHM inserts only fit VHM cylinder heads.

Which version should I choose?
Choose according to your engine and fuel. Version B (10.80 cc): 10.80 cc, piston height +1.75 mm, squish 1.10 mm; Version C (11 cc): 11.00 cc, piston height +1.75 mm, squish 1.10 mm; Version E (11.20 cc): 11.20 cc, piston height +1.75 mm, squish 1.10 mm; Version F (11.40 cc): 11.40 cc, piston height +1.75 mm, squish 1.10 mm; Version G (11.60 cc): 11.60 cc, piston height +1.75 mm, squish 1.10 mm.

Compatibility

Check the exact model and year of your bike in the list below before ordering.

Fits:
YAMAHA YZ 125 2000
YAMAHA YZ 125 1999
YAMAHA YZ 125 1998
YAMAHA YZ 125 1997
YAMAHA YZ 125 1996